# Urinary Tract Infections and Urosepsis

## Introduction

Urinary tract infections (UTIs) are among the most frequent infectious diagnoses in emergency medicine, accounting for approximately 10 million ED visits annually in the United States. The spectrum ranges from uncomplicated cystitis, a benign outpatient condition, to urosepsis with septic shock, which carries significant morbidity and mortality. The emergency physician must accurately distinguish uncomplicated from complicated UTIs, recognize risk factors for multidrug-resistant organisms, initiate appropriate empiric antibiotics, and identify the subset of patients who require emergent urologic intervention.

## Classification

### Uncomplicated UTI

Uncomplicated UTI is cystitis in a non-pregnant, immunocompetent, premenopausal woman with normal urologic anatomy. It is confined to the lower urinary tract and carries a low risk of complications, managed as an outpatient with oral antibiotics.

### Complicated UTI

Complicated UTI involves factors that increase treatment failure risk. These include anatomic abnormalities such as urethral stricture, vesicoureteral reflux, neurogenic bladder, and urinary diversions; obstruction from ureteral stones, BPH, or tumor; foreign bodies such as indwelling catheters and ureteral stents; and host factors including male sex, pregnancy, diabetes, immunosuppression, renal transplant, and elderly age. Upper tract involvement with pyelonephritis is also classified as complicated.

### Urosepsis

Urosepsis is sepsis originating from a urinary tract source and accounts for 20 to 30% of all sepsis cases. It is most commonly associated with obstructive uropathy from a ureteral calculus, BPH, or tumor with superimposed infection. Mortality reaches 20 to 40% when complicated by septic shock and is higher in the elderly and immunocompromised.

## Microbiology

Escherichia coli accounts for 75 to 95% of uncomplicated UTIs and 50% of complicated UTIs. Klebsiella pneumoniae is the second most common pathogen with increased prevalence in complicated UTIs. Proteus mirabilis is associated with struvite or staghorn stones and is a urease-producing organism. Enterococcus species are common in catheter-associated UTIs and are inherently resistant to cephalosporins. Pseudomonas aeruginosa is healthcare-associated and catheter-related, requiring antipseudomonal coverage. Staphylococcus saprophyticus is the second most common organism in young women with uncomplicated cystitis. ESBL-producing organisms and carbapenem-resistant Enterobacteriaceae have increasing prevalence, with risk factors including prior antibiotics, hospitalization, nursing home residence, and urinary catheter use.

<image>Diagram of the urinary tract showing ascending infection pathway from urethra to bladder (cystitis), up the ureters to the kidney (pyelonephritis), and into the bloodstream (urosepsis), with common pathogens listed at each anatomic level and risk factors for complicated infection annotated</image>

## Clinical Presentation

### Cystitis

Cystitis presents with dysuria, urinary frequency, urgency, and suprapubic pain or pressure. Gross hematuria may be present. Systemic symptoms such as fever, flank pain, and nausea are absent. In elderly patients, symptoms may be atypical, including confusion, functional decline, falls, and incontinence, but asymptomatic bacteriuria in the elderly should not be treated.

### Pyelonephritis

Pyelonephritis presents with fever often exceeding 38.5 degrees Celsius, chills and rigors, and costovertebral angle tenderness, which is the hallmark physical exam finding. Nausea and vomiting are common. Lower tract symptoms may or may not be present. Bacteremia occurs in 20 to 30% of pyelonephritis cases.

### Urosepsis

Urosepsis presents with sepsis criteria (qSOFA of 2 or more, SIRS criteria, or SOFA score elevation) from a urinary source, with hemodynamic instability including hypotension, tachycardia, and altered mental status. An obstructed, infected kidney is the most dangerous scenario, as infected urine under pressure requires emergent decompression.

## Diagnostic Evaluation

### Urinalysis and Urine Culture

Urinalysis shows pyuria with WBC of 10 or more per high-power field or positive leukocyte esterase, bacteriuria, and nitrites, which are specific but not sensitive since only gram-negative organisms produce them. Urine culture is the gold standard and should be obtained before antibiotics in all complicated UTIs, pyelonephritis, and recurrent infections; it is not necessary for uncomplicated cystitis. Clean-catch midstream specimens are used in most patients, with straight catheterization when a clean specimen cannot be provided. For catheter-associated UTI, specimens should be obtained from a freshly placed catheter, not the existing collection bag.

### Pitfall: Asymptomatic Bacteriuria

Asymptomatic bacteriuria is bacteria in the urine without urinary symptoms. It should not be screened for or treated in most populations, as treatment increases antibiotic resistance without clinical benefit. The exceptions requiring treatment are pregnant women, who face risk of pyelonephritis and preterm labor, and patients undergoing urologic procedures.

### Laboratory Studies for Complicated UTI/Urosepsis

CBC may show leukocytosis or leukopenia, with the latter concerning for severe sepsis. BMP assesses creatinine for AKI from obstruction or sepsis and electrolytes. Elevated lactate above 2 mmol/L indicates tissue hypoperfusion, and levels above 4 mmol/L are associated with high mortality. Blood cultures should be obtained in pyelonephritis, sepsis, and immunocompromised patients before antibiotics. Procalcitonin may help distinguish upper from lower UTI and guide antibiotic duration, with elevation in pyelonephritis and urosepsis.

### Imaging

CT abdomen and pelvis without contrast is indicated when urinary obstruction is suspected from a stone, mass, or abscess, and identifies hydronephrosis, perinephric abscess, and emphysematous pyelonephritis. Renal ultrasound is an alternative when CT is contraindicated, as in pregnancy, and identifies hydronephrosis but is less sensitive for stones and abscesses. Imaging is not needed for uncomplicated cystitis or uncomplicated pyelonephritis in young, healthy patients.

<image>CT scan showing obstructive pyelonephritis with a ureteral calculus at the ureterovesical junction causing proximal hydroureter and hydronephrosis, perinephric fat stranding, and annotations identifying the stone, dilated collecting system, and inflammatory changes requiring emergent urologic decompression</image>

## Treatment

### Uncomplicated Cystitis

| Condition | First-Line Antibiotic | Dose/Duration | Alternative |
|-----------|----------------------|---------------|-------------|
| Uncomplicated cystitis | Nitrofurantoin | 100 mg PO BID x 5 days | TMP-SMX DS PO BID x 3 days (if resistance < 20%) |
| Uncomplicated cystitis (alt) | Fosfomycin | 3 g PO x 1 dose | Cephalexin 500 mg PO QID x 7 days |
| Pyelonephritis (outpatient) | Ciprofloxacin | 500 mg PO BID x 7 days | TMP-SMX DS PO BID x 14 days (if susceptible) |
| Pyelonephritis (inpatient) | Ceftriaxone | 1 g IV daily | Piperacillin-tazobactam 3.375 g IV q6h |
| ESBL risk / urosepsis | Meropenem | 1 g IV q8h | Ertapenem 1 g IV daily |
| Catheter-associated UTI | Based on culture | 7–14 days | Remove or replace catheter first |

First-line agents per IDSA guidelines include nitrofurantoin 100 mg PO twice daily for 5 days (avoided if creatinine clearance is less than 30 mL/min), trimethoprim-sulfamethoxazole 160/800 mg PO twice daily for 3 days (if local resistance is less than 20%), and fosfomycin 3 g PO as a single dose (slightly less effective but convenient). Second-line agents are fluoroquinolones such as ciprofloxacin and levofloxacin, which should be reserved for complicated UTIs due to resistance concerns and side effect profile. Beta-lactams including amoxicillin-clavulanate and cephalexin are less effective for cystitis and should be used as a last line.

### Uncomplicated Pyelonephritis -- Outpatient

Outpatient management criteria include non-toxic appearance, ability to tolerate oral intake, reliable follow-up, and no complicating factors. Options include ciprofloxacin 500 mg PO twice daily for 7 days or levofloxacin 750 mg PO daily for 5 days if local fluoroquinolone resistance is less than 10%, and TMP-SMX 160/800 mg PO twice daily for 14 days if susceptibilities are known. A single dose of IM or IV ceftriaxone 1 g before discharge provides early bactericidal activity while oral antibiotics reach therapeutic levels.

### Complicated UTI and Pyelonephritis -- Inpatient

IV antibiotics include ceftriaxone 1 g IV daily, piperacillin-tazobactam 3.375 g IV every 6 hours, or meropenem 1 g IV every 8 hours for ESBL risk. Vancomycin should be added if Enterococcus is suspected based on catheter-related infection or gram-positive cocci on Gram stain. Transition to targeted oral therapy is appropriate once sensitivities are available and the patient is clinically improving, defined as afebrile for more than 48 hours and tolerating oral intake.

### Urosepsis Management

The SEP-1 bundle should be initiated with lactate measurement, blood cultures, broad-spectrum antibiotics within 1 hour, and fluid resuscitation with 30 mL/kg crystalloid for hypotension or lactate of 4 or higher. Source control is critical: an obstructed, infected kidney requires emergent decompression via percutaneous nephrostomy tube by interventional radiology or ureteral stent placement by urology. Decompression should occur within hours, not days, as delay increases mortality. Vasopressors with norepinephrine as first-line are used for septic shock refractory to fluid resuscitation. ICU admission is indicated for hemodynamic instability, organ failure, or need for vasopressors.

## Special Populations

### Pregnancy

Asymptomatic bacteriuria should be screened for and treated with a culture at the first prenatal visit. Safe antibiotics include nitrofurantoin (avoided near term), cephalexin, and amoxicillin-clavulanate. Fluoroquinolones (cartilage toxicity) and TMP-SMX (folate antagonism in first trimester, kernicterus risk near term) should be avoided. A low threshold for admission is warranted with pyelonephritis in pregnancy due to preterm labor risk.

### Catheter-Associated UTI (CAUTI)

The catheter should be removed or replaced before obtaining a culture, as biofilm on old catheters skews results. Only symptomatic CAUTI should be treated, not catheter-associated asymptomatic bacteriuria. Treatment duration is 7 days for patients with prompt resolution and 10 to 14 days for delayed response.

### Emphysematous Pyelonephritis

This gas-forming infection of the renal parenchyma occurs most commonly in poorly controlled diabetics. CT is diagnostic, showing gas within the renal parenchyma or perinephric space. Mortality reaches 20 to 40%, and management requires emergent IV antibiotics, percutaneous drainage, and possible nephrectomy.

## Clinical Pearls

Asymptomatic bacteriuria in the elderly should not be treated, as confusion alone is not a UTI symptom, and this practice drives antibiotic resistance without improving outcomes. An obstructed, infected kidney (pyonephrosis) is a urologic emergency requiring emergent decompression, as antibiotics alone are insufficient. Nitrofurantoin and TMP-SMX are first-line for uncomplicated cystitis, and fluoroquinolones should be reserved for complicated infections and pyelonephritis. Blood cultures and urine culture should always be obtained before antibiotics in complicated UTI, pyelonephritis, and urosepsis. A single IV dose of ceftriaxone before discharge provides a safety net for patients being treated as outpatients for pyelonephritis.

## References

1. Gupta K, et al. "International Clinical Practice Guidelines for the Treatment of Acute Uncomplicated Cystitis and Pyelonephritis in Women: A 2010 Update by the IDSA and ESMID." *Clinical Infectious Diseases*. 2011;52(5):e103-e120.
2. Wagenlehner FM, et al. "Diagnosis and Management for Urosepsis." *International Journal of Urology*. 2013;20(10):963-970.
3. Nicolle LE, et al. "Clinical Practice Guideline for the Management of Asymptomatic Bacteriuria: 2019 Update by IDSA." *Clinical Infectious Diseases*. 2019;68(10):e83-e110.
4. Foxman B. "Urinary Tract Infection Syndromes: Occurrence, Recurrence, Bacteriology, Risk Factors, and Disease Burden." *Infectious Disease Clinics of North America*. 2014;28(1):1-13.